Low energy electron diffraction studies of the surfaces of molecular crystals (ice, ammonia, naphthalene, benzene)

Abstract

Low Energy Electron Diffraction (LEED) has been used to study the surface structures of thin films of molecular crystals. The samples were grown epitaxially on metal single crystal substrates at low temperatures. Both Pt(111) and Ag(111) surfaces were used as substrates in order to identify the influence of the substrate on molecular film structure. Previous observations of ice (0001) and naphthalene (001) surfaces on films grown on Pt(111) substrates [Surface Sci. 55 (1976) 413], were confirmed using the Ag(111) substrate. The NH 3(111) and benzene (111) surfaces were also studied on films grown on either substrate. All observed molecular crystal surfaces showed no evidence of surface reconstruction. To minimize sample charging and electron beam induced damage, LEED experiments were performed on samples of thickness less than 10−10 2 nm, with low energy electron exposures less than 1 C cm −2. The maximum thickness and exposure values were characteristic of the particular molecular crystal. The relationship between the structure of the initial adsorbed monolayer and the molecular crystal orientation is discussed.